Water-absorbing polymers having supramolecular hollow molecules, method for producing them and use of the same

ABSTRACT

The invention relates to absorbent polymers based on optionally partially neutralised, monoethylenically unsaturated, acid group-carrying monomers. The surfaces of said polymers are re-cross-linked. The inventive polymers also have cyclodextrines and/or cyclodextrine derivatives which are covalently and/or ionically bonded and/or included therein.

The invention relates to absorbents, preferably for water and aqueousliquids, which absorbents are based on polymers absorbing aqueousliquids, wherein cyclodextrin or cyclodextrin derivatives have beenincorporated tonically, covalently and/or as a result of mechanicalinclusion.

Commercially available superabsorbing polymers essentially arecrosslinked polyacrylic acids, crosslinked starch/acrylic acid graftcopolymers, crosslinked hydrolyzed starch/acrylonitrile graftcopolymers, crosslinked poly-(maleic anhydride-co-isobutylene), ormixtures of various of the above-mentioned crosslinked polymers, whereinthe carboxylic groups have been subjected to partial neutralization withsodium and/or potassium ions.

Such polymers find use e.g. in hygiene articles capable of absorbingbody fluids such as urine or in materials for cable sheathings wherethey absorb large amounts of aqueous liquids and body fluids such asurine or blood with swelling and formation of hydrogels. Furthermore,the absorbed amount of liquid must be retained under a pressure typicalof use. During the further technical development of superabsorbingpolymers, the pattern of requirements to be met by these products haschanged significantly over the years. To date, the development ofsuperabsorbers has been forced particularly with respect to the amountof absorbed liquid and pressure stability.

Such crosslinked polymer products based on monomers containing acidgroups are obtained by using one or more primary crosslinkers and one ormore secondary crosslinkers and exhibit a combination of properties,namely, high retention, high absorption under pressure, low solubles,and rapid absorption of liquid, which has not been achieved so far. Whenused in hygiene articles, these crosslinked polymer products have theadvantage that secreted fluids, once absorbed by the polymer product,can no longer contact the skin. Thus, skin lesions such as diaperdermatitis can largely be avoided. Such comfort can even be increased byabsorbing malodorous compounds.

According to Römpp Chemie Lexikon, the content of urine components issubject to physiological fluctuations; also, particular substances aresecreted at concentrations varying within a daily period, so that moreprecise data on the urine composition invariably are related to theso-called 24 hour urine which, in a healthy adult, contains e.g. urea(average 20 g), uric acid (0.5 g), creatinine (1.2 g), ammonia (0.5 g),amino acids (2 g), proteins (60 mg), reducing substances (0.5 g, about70 mg of which are D-glucose or urine sugar), citric acid (0.5 g) andother organic acids, as well as certain vitamins (C, B₁₂ etc.). Thefollowing inorganic ions are present: Na⁺ (5.9 g), K⁺ (2.7 g), NH₄ ⁺(0.8 g), Ca²⁺ (0.5 g), Mg²⁺ (0.4 g); Cl⁻ (8.9 g), PO₄ ³⁻ (4.1 g), SO₄ ⁻²(2.4 g). The dry content is between 50 and 72 g. Inter alia,alkylfurans, ketones, lactones, pyrrole, allyl isothiocyanate, anddimethyl sulfone have been recognized as volatile components of urine.Most of the volatile components are molecules having a molar mass belowabout 1000 g/mol and a high vapor pressure.

Volatile components of urine have also been investigated by, inter alia,A. Zlatkis et al. (Anal. Chem. Vol. 45, 763ff.). It is also well-knownthat consumption of asparagus results in an increase of theconcentration of organic sulfur-containing compounds in human urine (R.H. Waring, Xenobiotika, Vol. 17, 1363ff.). In patients who are subjectto specific diets and generally, in patients who ingest specificmedications, or in elderly individuals with decreasing kidney function,the urine may include malodorous substances. Patients suffering fromurine incontinence have an increased secretion of ureases which convertthe urea contained in urine, thereby liberating toxic ammonia. Also, apathological change is well-known which is referred to as fish smellsyndrome. It results from an increased secretion of quaternary ammoniumcompounds.

Previous approaches of achieving an odor reduction in incontinenceproducts are based on reducing the concentration of free ammonia.Basically, there are two approaches to this end: preventing additionalproduction of ammonia from urea degradation by suitable ureaseinhibitors (A. Norberg et al., Gerontology, 1984, 30, 261ff.), or byprotonating free ammonia and binding thereof in the form of acarboxylate ammonium salt. This method is disadvantageous in thatessentially, merely ammonia and other nitrogen-containing components canbe controlled. Malodorous compounds lacking basic groups, e.g. thiols,are still capable of entering the vapor space.

It is well-known to those skilled in the art that certain hollowmolecules, also referred to as endohedral or concave molecules, arecapable of incorporating other, mostly smaller, so-called guestmolecules, thereby forming a host-guest complex. Such complex formationhas an effect on the chemical and physical properties of both guest andhost molecule. These hollow-forming molecules include the cyclodextrins.

Cyclodextrins are formed during starch degradation by Bacillus maceransor Bacillus circulans under the action of cyclodextrin glycosyltransferase. They are comprised of 6, 7, 8 or 9 glucose unitsα-1,4-linked to form a ring (α-, β- or γ-cyclodextrins) They are capableof entrapping hydrophobic guest molecules in varying amounts up tosaturation (“molecular encapsulation”), e.g. gases, alcohols orhydrocarbons. The use of cyclodextrins as host molecule is reportedcomprehensively in the work of J. Szejtli (Cyclodextrin Technology,Kluwer Academic Publishers, 1988).

Also, the production of polymers containing cyclodextrins is alreadyknown. Thus, EP-A-0,483,380 obtains cyclodextrin-containing polymers bycopolymerizing cyclodextrins bearing aldehyde groups with polyvinylalcohol.

Crosslinked, water-swellable, hydrophilic bead polymers made ofhydroxyalkylcyclodextrins and epichlorohydrin or polyepoxide typecrosslinkers are known from U.S. Pat. No. 5,360,899. These crosslinkersinvolve a carcinogenic potential and therefore, such products cannot beused in hygiene articles. These cyclodextrins immobilized bypolymerization are used as packing and separating material inchromatographic separation columns.

Furthermore, water-swellable, hydrophilic bead polymers made ofcyclodextrins bearing glycidyl or methacrylate groups and optionallyother comonomers such as hydroxyethyl acrylate are known from U.S. Pat.No. 5,357,012. Likewise, these cyclodextrins immobilized bypolymerization are used as packing and separating material inchromatographic separation columns.

DE-A-195 20 989 describes covalent binding of reactive cyclodextrinderivatives having at least one nitrogen-containing heterocycle topolymers bearing at least one nucleophilic group. Polymers linked tocyclodextrins according to this method must have nucleophilic groupssuch as OH, NH, or SH groups. Also, polymerizable cyclodextrinderivatives are mentioned which, after suitable modification, arecopolymerized with other monomers, e.g. ethylenically unsaturatedcompounds. As noted in this publication, the products according to theabove-mentioned U.S. patent specifications U.S. Pat. Nos. 5,357,012 and5,360,899 involve the drawback that cyclodextrin incorporation isdifficult to control in spatial terms and that cyclodextrins fixedinside the polymers are no longer available for utilization. The use ofpolymers, which include cyclodextrin derivatives, as superabsorbingmaterials is not mentioned.

Inter alia, the use of cyclodextrins in hygiene products is known fromEP-A-806,195, WO 94/22501, and WO 94/22500. Therein, the cyclodextrinsare employed to absorb odors. In those cases where the cyclodextrins orcyclodextrin complexes are not bound to the powdered absorbent, demixingduring storage or transportation of the hygiene articles may occur. As aresult, the effectiveness of the cyclodextrins as odor absorbent may belost due to demixing between absorbent and cyclodextrins.

To achieve improved adhesion on powdered absorbents, WO 94/22501 teachesaddition of polyethylene glycols or other linear polymers tocyclodextrin in a “melt” or in solution and subsequent spraying on thepowdered absorbent. However, as is well-known to those skilled in theart, linear polymers have a marked tendency to thread into thecyclodextrin cavity, which fact is advantageously utilized insupramolecular chemistry in order to produce e.g. rotaxans or catenanes(cf. the documents U.S. Pat. No. 5,538,655; G. Wenz, Angew. Chem. 1994,106, 851). Typically, the linear polymers have a molecular weight (m.w.)of more than 200. Also, suitable polymers are e.g. polyethylene glycol(PEG), polypropylene oxide (PEO) and polyethyleneimine. Multiplecyclodextrins can be threaded on a linear polymer chain; Harada et al.(J. Org. Chem. 58, 1993, 7524-28) report that 20 cyclodextrins can bethreaded on a polyethylene glycol having an average molecular weight of2000 g/mol. Therefore, the process described in WO 94/22501 isparticularly disadvantageous, because the cyclodextrin cavities aftersuch a polyethylene glycol pre-treatment are no longer quantitativelyavailable for absorbing malodorous compounds.

The invention therefore is based on the object of providing polymerproducts capable of absorbing water or aqueous liquids, and capable ofbinding malodorous organic compounds such as occurring e.g. in urine orother fluids secreted from the body, and methods of producing same.

The polymer products should not involve the drawbacks of prior art andenable a preferably uniform, marked reduction of gaseous, malodorouscompounds released during use. Moreover, a largely stable dispersion ofthe deodorant component in the absorbent should be achieved, i.e.,demixing prior to and during use should be avoided as much as possible.In addition, binding of the deodorant component should not be effectedby using carcinogenic or otherwise hazardous substances. Furthermore,the effectiveness of the deodorant component in the absorbent should beindependent of its location, i.e., whether inside the polymer or at thesurface thereof.

According to the invention, said object is accomplished by providingpolymers based on crosslinked monomers bearing optionally partiallyneutralized acid groups, which polymers have cyclodextrins and/orderivatives thereof bound ionically and/or covalently and/orincorporated therein.

As a result of the inventive binding to the preferably powdered polymer,the cyclodextrin component can be extracted by the liquid to be absorbedto only a lesser extent, or, in the dry state, undergoes demixing toonly a lesser extent. Despite the intimate linkage with the crosslinkedabsorber bearing acid groups, the polymer according to the inventionsurprisingly shows excellent absorption of odors which is even enhancedcompared to unbound cyclodextrin. In particular, the absorbent polymersexhibit high absorption of odors even in those cases where thecyclodextrin is fixed inside the absorber. This can be established by aneffective reduction in the gas concentration of malodorous substances.

Moreover, the polymer products of the invention are excellently suitedfor incorporating active substances, and when used, these activesubstances can optionally be released in a controlled fashion. Byincorporation in the absorbents of the invention, the stability ofsensitive active substances is markedly improved.

According to the invention, α,β,γ type cyclodextrins and derivativesthereof are suitable.

The cyclodextrins have the following recurring structure:

The anhydroglucose units are linked in a cyclic, glycosidic fashion toform rings, wherein the residues R₁ through R₃ are the same ordifferent, represent H or C₁-C₄ alkyl, and α-cyclodextrin: n=6,β-cyclodextrin: n=7, γ-cyclodextrin: n=8, δ-cyclodextrin: n=9. Incyclodextrin derivatives, n different substituents per residue (R₁-R₃)are possible which may be the same or different.

Above all, those derivatives are possible which permit chemical linkageby ionic or covalent binding to the monomer bearing acid groups or tothe corresponding polymer. Covalent linkages preferably are via C—Cbonds as, for example, with cyclodextrin derivatives havingethylenically unsaturated groups incorporated covalently in the polymerchain already during polymerization of the monomers. For example, suchgroups are (meth)acrylic, (meth)allyl and vinyl groups. According to theinvention, however, covalent linkage of the cyclodextrin component tothe polymer of ethylenically unsaturated monomers is also possiblesubsequent to polymerization via ether, amide or ester groups.

Ionic binding of the cyclodextrin derivatives can be effected usinganionic or cationic groups, with cationic groups being preferred.Frequently, it is advantageous when the cyclodextrin molecules havemultiple substitutions with ionic groups. Examples of anionic groups arecarboxylate, sulfate and sulfonate groups. Examples of cationic groupsare quaternary groups containing nitrogen.

Ionic cyclodextrins can be produced by reacting cyclodextrin derivativeswith reactive compounds such as chloroacetic acid, sodium chloroacetate,maleic acid, maleic anhydride, and succinic anhydride. In an aqueoussolution, these reaction products, e.g. carboxymethylcyclodextrin, carrya negative charge in a basic medium due to the carboxylate group.

Cyclodextrin derivatives to be used according to the invention andhaving at least one nitrogen-containing heterocycle can be producedaccording to the teaching of DE-A-195 20 98, A1, the disclosure of whichis hereby incorporated by reference. In this way, cyclodextrinderivatives can be obtained, which include another group active towardsnucleophilic groups. These derivatives can undergo direct reaction withpolymers bearing nucleophilic groups. Examples of nucleophilic groupsare —OH, —NH or —SH groups.

Other chemically modified cyclodextrins to be used according to theinvention can be obtained as described in A. P. Croft and R. A. Bartsch,Tetrahedron Vol. 39, No. 9, pp. 1417-1473. They are obtained by reactingnitrogen-containing compounds having at least one functional groupcapable of reacting with the hydroxyl groups of the cyclodextrins toform ether, ester or acetal groups.

Cationic cyclodextrins such as described in Ch. Roussel, A. Favrou,Journal of Chromatography A, 704 (1995), 67-74, are particularlypreferred. They are obtained by reacting cyclodextrin with e.g.N-(3-chloro-2-hydroxypropyl)-N,N,N-trimethylammonium chloride. Thecyclodextrins described in the above publication have a degree ofsubstitution of 0.2.

The ionic cyclodextrins including at least one nitrogen-containingaliphatic residue, which can be used according to the invention, mayalso be produced e.g. according to the methods described in U.S. Pat.Nos. 3,740,391; 4,153,585 and 4,638,058. The disclosure of theabove-mentioned publications is hereby incorporated by reference.

For example, N,N-dimethylaminoethyl (:meth)acrylate,N,N-dimethylaminopropyl (meth)acrylate,N,N-dimethylaminoethyl(meth)acrylamide, andN,N-dimethylaminopropyl(meth)-acrylamide, or the quaternary derivativesthereof obtained by reaction with alkyl halides may be mentioned assuitable monomers. Preferably, N,N-dimethylaminoethyl acrylate (ADAME orADAME-quat.) and N,N-dimethylaminopropylacrylamide (DIMAPA orDIMAPA-quat.) are employed.

Here, the compound of formula I undergoes reaction:H₂C═CR¹—CO—X—R²—N⁺(R³)₃Y⁻  (I)wherein

-   -   R¹=H, CH₃,    -   R²=C₂-C₄ alkylene group,    -   R³=H, C₁-C₄ alkyl group,    -   X=0, NH,    -   Y=Cl, SO₄.

The average degree of substitution (DS value) per anhydroglucose unitfor substituents containing nitrogen can be determined according tomethods known from literature using elemental analysis as described e.g.in U.S. Pat. Nos. 5,134,127 and 3,453,257 for substituents containingsulfur or nitrogen. When using the synthetic methods described in U.S.Pat. Nos. 3,740,391 and 4,153,585, the DS value can be varied withinwide limits.

3 hydroxyl groups per anhydroglucose unit of a cyclodextrin are capableof undergoing further reaction. Therefore, the degree of substitutione.g. in case of β-cyclodextrin can be between 0.05 and 3 at maximum. Adegree of substitution below 0.05 indicates that a mixture ofnon-modified cyclodextrin and chemically modified cyclodextrin ispresent.

According to the invention, the degree of substitution (DS) of thecyclodextrin derivatives is 0.005-2, preferably 0.05-1.5.

In addition to the above-mentioned groups required for binding to thepolymer, the cyclodextrins may also contain other substituents having noreactivity towards the polymer. For example, these include reactionproducts of cyclodextrins with alkylating agents, e.g. C₁-C₂₂ alkylhalides, e.g. methyl chloride, ethyl chloride, butyl chloride, butylbromide, benzyl chloride, lauryl chloride, stearyl chloride, or dimethylsulfate, or reaction products of cyclodextrins with alkylene oxides suchas ethylene oxide, propylene oxide, butylene oxide, or styrene oxide.

The amount of cyclodextrin or derivatives thereof to be employedaccording to the invention is 0.01-50 wt.-%, preferably 0.1-30 wt.-%,more preferably 0.5-10 wt.-%, relative to the total amount of polymer.

Well-known processes are possible for polymerizing the polymers of theinvention optionally having superabsorbent properties, e.g. bulkpolymerization, solution polymerization, spray polymerization, inverseemulsion polymerization, and inverse suspension polymerization.

Preferably, a solution polymerization is performed using water assolvent. The solution polymerization may be conducted in a continuous orbatchwise fashion. The prior art includes a broad spectrum of possiblevariations with respect to concentration conditions, temperatures, typeand amount of initiators and of secondary catalysts. Typical processeshave been described in the following patent specifications: U.S. Pat.No. 4,286,082; DE 27 06 135, U.S. Pat. No. 4,076,663, DE 35 03 458, DE40 20 780, DE. 42 44 548, DE 43 23 001, DE 43 33 056, DE 44 18 818 whichhereby are incorporated as disclosure of the process according to theinvention.

Preferably, aliphatic, optionally substituted C₂-C₁₀, preferably C₂-C₅carboxylic acids or sulfonic acids, such as acrylic acid, methacrylicacid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid,itaconic acid, vinylacetic acid, vinylsulfonic acid, methallylsulfonicacid, 2-acryl-amido-2-methyl-1-propanesulfonic acid, as well as thealkali and/or ammonium salts or mixtures thereof are possible asethylenically unsaturated monomers containing acid groups. It ispreferred to use acrylic acid and its alkali and/or ammonium salts andmixtures thereof. Furthermore, it is also possible to use monomers beinghydrolyzed to form acid groups as late as subsequent to thepolymerization, e.g. the corresponding nitrile compounds.

In order to modify the polymer properties, up to 40 wt.-% of monomersother than the monomers containing acid groups, which are soluble in theaqueous polymerization batch, such as acrylamide, methacrylamide,acrylonitrile, (meth)allyl alcohol ethoxylates, and mono(meth)acrylicacid esters of polyhydric alcohols or ethoxylates can optionally beused.

Minor amounts of crosslinking monomers having more than one reactivegroup in their molecules are copolymerized together with theabove-mentioned monomers, thereby forming partially crosslinked polymerproducts which are no longer soluble in water but merely swellable. Bi-or multifunctional monomers, e.g. methylenebisacryl- or -methacrylamide,or ethylenebisacrylamide may be mentioned as crosslinking monomers, andalso, allyl compounds such as allyl (meth)acrylate, alkoxylated allyl(meth)acrylate reacted preferably with from 1 to 30 mol of ethyleneoxide units, triallyl cyanurate, maleic acid diallyl ester, polyallylesters, tetraallyloxyethane, triallylamine, tetraallylethylenediamine,allyl esters of phosphoric acid or phosphorous acid, and also, theN-methylol compounds of unsaturated amides such as methacrylamide oracrylamide and the ethers derived therefrom, as well as esters ofpolyols and alkoxylated polyols with unsaturated acids, such asdiacrylates or triacrylates, e.g. butanediol or ethylene glycoldiacrylate, polyglycol di(meth)acrylates, trimethylolpropanetriacrylate, di- and triacrylate esters of trimethylolpropane preferablyoxyalkylated (ethoxylated) with 1 to 30 mol alkylene oxide, acrylate andmethacrylate esters of glycerol and pentaerythritol, and of glycerol andpentaerythritol preferably oxyethylated with 1 to 30 mol ethylene oxide.It is preferred to use triallylamine, acrylates of polyhydric alcoholsor alkoxylates thereof, and methallyl alcohol acrylates or alkoxylatesthereof. The ratio of crosslinking monomers is from 0.01 to 3.0 wt.-%,preferably from 0.05 to 2.0 wt.-%, and more preferably from 0.05 to 1.5wt.-%, relative to the total weight of the monomers.

The optional neutralization of the acidic monomers according to thepolymerization process of the invention can be performed in variousways. On the one hand, according to the teaching of U.S. Pat. No.4,654,039, the polymerization may be conducted directly with the acidicmonomers, with neutralization being effected subsequently in the polymergel. Preferably, the acid groups of the monomers are already neutralizedto 20-95%, preferably 50-80% prior to polymerization, in which case theyare present as sodium and/or potassium and/or ammonium salts at the timepolymerization is begun. It is preferred to use those bases forneutralization which do not adversely affect the subsequentpolymerization. It is preferred to use sodium or potassium hydroxidesolution and/or ammonia, with sodium hydroxide solution beingparticularly preferred; addition of sodium carbonate, potassiumcarbonate or sodium bicarbonate may have an additional positive effectas taught in U.S. Pat. Nos. 5,314,420 and 5,154,713. Before initiatingthe polymerization in this adiabatic solution polymerization, thepartially neutralized monomer solution is cooled to a temperature ofbelow 30° C., preferably below 20° C. The other polymerization processescomply with the temperatures known from prior art as apparent from theliterature below.

The polymer products of the invention may optionally containwater-soluble natural or synthetic polymers as a basis for grafting inamounts up to 30 wt.-%. Inter alia, these include partially orcompletely saponified polyvinyl alcohols, starch or starch derivatives,cellulose or cellulose derivatives, polyacrylic acids, polyglycols, ormixtures thereof. The molecular weights of the polymers added as basisfor grafting must be adapted to the circumstances of the polymerizationconditions. In the event of an aqueous solution polymerization, forexample, it may be necessary for viscosity reasons to employ low tomedium molecular weight polymers, whereas this factor plays a minor rolein a suspension polymerization.

In addition to polymers obtained by crosslinking polymerization ofpartially neutralized acrylic acid, those are preferably used which areobtained by employing starch or polyvinyl alcohol as graft basis.

The polymerization process of the invention can be initiated by variousconditions, e.g. by irradiating with radioactive, electromagnetic orultraviolet radiation, or by a redox reaction of two compounds, e.g.sodium hydrogen sulfite with potassium persulfate, or ascorbic acid withhydrogen peroxide. The thermally induced decomposition of a so-calledfree-radical initiator such as azobisisobutyronitrile, sodiumperoxodisulfate, t-butyl hydroperoxide, or dibenzoyl peroxide issuitable as well. Furthermore, a combination of some of theabove-mentioned polymerization initiators is possible.

Preferably, the polymer products of the invention are produced accordingto two methods:

According to the first method, the partially neutralized acrylic acid isconverted to a gel by means of free-radical polymerization in aqueoussolution and in the presence of crosslinkers and optional polymeradditives, which gel is subsequently crushed and dried until a powdered,flowable state is reached, milled, and screened to the desired particlesize. The solution polymerization may be conducted in a continuous orbatchwise fashion. The patent literature includes a broad spectrum ofpossible variations with respect to concentration conditions,temperatures, type and amount of initiators, as well as a variety ofsecondary crosslinking options. Typical processes have been described inthe following patent specifications: U.S. Pat. Nos. 4,076,663;4,286,082; DE 27 06 135, DE 35 03 458, DE 35 44 770, DE 40 20 780, DE 4244 548, DE 43 23 001, DE 43 33 056, DE 44 18 818, the disclosure ofwhich is hereby incorporated by reference.

The inverse suspension and emulsion polymerization process may also beused to produce the polymer products of the invention. According to thisprocess variant, an aqueous, partially neutralized solution of acrylicacid is dispersed in a hydrophobic organic solvent using protectivecolloids and/or emulsifiers, and the polymerization is initiated usingfree-radical initiators. The crosslinkers are either dissolved in themonomer solution and pre-charged together with same or added separatelyand optionally during polymerization. The optionally present polymericgrafting bases are added via the monomer solution or by directly placingin the oil phase. Subsequently, the water is removed azeotropically fromthe mixture, and the polymer product is filtrated and optionally dried.

Using the process of subsequent surface crosslinking, the polymerproducts according to the invention are improved in their pattern ofproperties, particularly in their absorption of liquid under pressure,so that the well-known phenomenon of “gel blocking” is suppressed, whereslightly swollen polymer particles adhere to each other, therebyimpeding further absorption of liquid and distribution of liquid in theabsorbent articles. In this secondary crosslinking, the carboxyl groupsof the polymer molecules are crosslinked at the surface of the polymerparticles at elevated temperature using crosslinking agents. Inter alia,methods of secondary crosslinking have been described in the followingpublications: DE 40 20 780, EP 317,106 and WO 94/9043. According to theinvention, all those surface crosslinking agents known to a personskilled in the art from U.S. Pat. No. 5,314,420, page 8, lines 3-45, maybe employed advantageously in combination with a crosslinker used duringpolymerization or a combination of crosslinkers. As a rule, thesecompounds contain at least two functional groups capable of reactingwith carboxylic acid or carboxyl groups. Alcohol, amine, aldehyde, andcarbonate groups are preferred and also, crosslinker molecules havingmultiple different functions are employed. Preferably, polyols,polyamines, polyaminoalcohols, and alkylene carbonates are used.Preferably, one of the following crosslinking agents is used: ethyleneglycol, diethylene glycol, triethylene glycol, polyethylene glycol,glycerol, polyglycerol, propylene glycol, diethanolamine,triethanolamine, polypropylene glycol, block copolymers of ethyleneoxide and propylene oxide, sorbitan fatty acid esters, ethoxylatedsorbitan fatty acid esters, trimethylolpropane, ethoxylatedtrimethylolpropane, pentaerythritol, ethoxylated pentaerythritol,polyvinyl alcohol, sorbitol, ethylene carbonate, propylene carbonate. Itis particularly preferred to use polyols and ethylene carbonate assurface crosslinking agents. The crosslinking agent is employed in anamount of from 0.0.1 to 30 wt.-%, preferably 0.1-10 wt.-%, relative tothe polymer to be crosslinked.

Following polymerization, the polymer product is dried, milled, screenedfor the respective grain fraction favorable in application-technicalterms, and subsequently subjected to surface crosslinking. In somecases, however, it has proven beneficial to add the surface secondarycrosslinkers at an early stage prior to drying the polymer gel or priorto crushing the partially or predominantly dried-polymer. Secondarycrosslinking to be performed according to the invention has beendescribed in U.S. Pat. No. 4,666,983 and DE 40 20 780 which hereby areincorporated by reference. Advantageously, the secondary crosslinkerfrequently is added in the form of a solution in water, organic solventsor mixtures thereof, particularly in those cases where low amounts ofsecondary crosslinking agent are used. Suitable mixing apparatus forapplying the secondary crosslinking agent are, e.g., Patterson-Kelleymixers, DRAIS turbulence mixers, Lödige mixers, Ruberg mixers, screwmixers, pan mixers, and fluid-bed mixers, as well as continuouslyoperated vertical mixers wherein the powder is mixed at a rapidfrequency using rotating knives (Schugi mixer). Once the surfacecrosslinker has been mixed with the crosslinked polymer, heating totemperatures of from 60 to 250° C., preferably from 135 to 200° C., andmore preferably from 150 to 185° C. is effected in order to perform thesurface crosslinking reaction. The time period of the heat treatment islimited by the risk of destroying the desired pattern of properties ofthe superabsorbent polymer product as a result of heat damage.

Depending on the type of use, various screening fractions are employedfor processing the polymer products as superabsorbers, e.g. between 100and 1000 μm and preferably between 150 and 850 μm for diapers. Ingeneral, this grain fraction is produced by milling and screening priorto and/or subsequent to secondary crosslinking.

According to the process of the invention, the cyclodextrins orderivatives thereof are employed as substance or dissolved in a solvent.A preferred solvent is water, but mixtures of water and organic solventssuch as ethyl alcohol, acetone are also used.

The addition of the cyclodextrin component can be effected at variousprocess stages in the production of the polymer products according tothe invention. The amount of cyclodextrins or derivatives thereof is0.01-50 wt.-%, preferably 0.1-30 wt.-%, and more preferably 0.5-10wt.-%, relative to the amount of polymer product.

Thus, addition to the monomer solution is possible, where thecyclodextrin or its derivative is added directly to the aqueous monomersolution prior to the polymerization thereof. In case the polymerproduct of the invention is produced by suspension polymerization, it isalso possible to pre-charge all or part of the cyclodextrin in the oilphase and meter the monomer solution thereto. Where only a part of thecyclodextrin is pre-charged, the remainder can be introduced via themonomer solution.

It is also possible to apply the cyclodextrin component onto a non-driedpolymer gel, where the cyclodextrin or its derivative as substance ordissolved in water and/or an organic solvent is applied onto the crushedpolymer gel, preferably by spraying and mixing.

However, it is also possible to dry and crush the polymer gel initially,and subsequently apply the cyclodextrin or its derivative as substanceor dissolved in water and/or an organic solvent onto the powder. Theresulting product immediately can be processed further or dried toremove solvents.

The cyclodextrin component may also be added onto the crushed and driedabsorbent material during surface crosslinking of the polymer product.Suitable mixing apparatus for applying the crosslinking agent and thecyclodextrin component are e.g. Patterson-Kelley mixers, DRAISturbulence mixers, Lödige mixers, Ruberg mixers, screw mixers, panmixers, and fluid-bed mixers, as well as continuously operated verticalmixers wherein the powder is mixed at a rapid frequency using rotatingknives (Schugi mixer).

Also, the cyclodextrin component can be applied onto the crushed,already surface-crosslinked polymer product. In this process variant,according to the invention, preferably ionically modified cyclodextrinsas substance or dissolved in water and/or an organic solvent are sprayedonto the preferably powdered polymer, followed by evaporating thesolvent.

According to the process of the invention, the cyclodextrin componentmay also be introduced at various stages of the production process, soas to optionally optimize its effect. In this way it is possible, forexample, to polymerize a non-modified cyclodextrin together with themonomer solution and fix an ionically modified cyclodextrin on thesurface of the polymer during surface crosslinking.

It is also possible to bind the cyclodextrin component to the polymer inan additional surface crosslinking.

Using the methods according to the invention, final products areobtained wherein the cyclodextrin or its derivative is incorporated inthe synthetic polymer in such a way that the amount of cyclodextrinextractable with water is significantly less than the amount actuallycontained in the final product. In the products according to theinvention, the extractable percentage of cyclodextrins is below 85% ofthe amount present in the product, preferably 60%, and more preferably45%.

Owing to their excellent absorptive capacity, the polymer products ofthe invention are suitable as absorbents which, compared to powderedabsorbents including no cyclodextrin or derivative thereof, exhibitimproved absorption of malodorous compounds.

The polymers according to the invention find use e.g. in hygienearticles capable of absorbing body fluids such as urine, or in thepackaging sector, e.g. meat and fish products, where they absorb largeamounts of aqueous liquids and body fluids such as urine or blood, withswelling and formation of hydrogels. The polymer products of theinvention are incorporated directly as powders in constructions forabsorbing liquids, or previously fixed in foamed or non-foamed sheetmaterials. For example, such constructions for absorbing liquids arediapers for babies, incontinence articles or absorbent inserts inpackaging units for foodstuffs.

Moreover, the absorbents of the invention were found to be excellentlysuited for incorporating active substances. The stability of sensitiveactive substances, e.g. with respect to oxidative degradation, issubstantially improved as a result of incorporation in the absorbents ofthe invention.

Furthermore, the polymers according to the invention find use in plantbreeding and in pest control in agriculture. In plant breeding, thepolymers in the vicinity of plant roots provide for sufficient supply ofliquid and previously incorporated nutrients and are capable of storingand releasing same over a prolonged period of time.

In pest control, the polymers can incorporate single active substancesor a combination of multiple active substances which in use are releasedin a controlled fashion in terms of time and amount.

Production and properties of the polymer products according to theinvention will be illustrated in the following Examples which alsocomprise the production of ionic cyclodextrins used according to theinvention.

Test Methods Used on Polymers According to the Invention:

-   1) 180 ml of an aqueous solution of sodium chloride is poured over 1    g of polymer product, and this is stirred thoroughly for 1 hour    (alternatively 16 hours) at room temperature. This is subsequently    filtrated through a screen, and the concentration of cyclodextrin is    determined according to the method below. This method is based on    the reduction of light absorption (550 nm) of an alkaline solution    of phenolphthalein in the presence of cyclodextrin which, as    described by T. Takeuchi and T. Miwa, Chromatographia 1994, 38, 453,    can be determined. The concentration obtained experimentally is    divided by the concentration calculated theoretically. The    theoretical concentration can be determined from the amount of    cyclodextrin employed in the powder by dividing by 180. In this way,    the extracted amount of cyclodextrin is obtained.    ${{EA}\quad({CD})} = \frac{{Concentration}\quad({CD})\quad{found}}{{Theoretical}\quad{concentration}\quad({CD})}$    EA(CD): extractable percentage of cyclodextrin.-   2) Determination of the absorption of malodorous compounds

0.1 g of powdered polymer product is added with 2 ml of an aqueoussolution (including 5 wt.-% ethanol) of malodorous compound, and this issealed in a 5 ml test vessel. This is allowed to stand at 40° C. for 20minutes, and the content of malodorous compound in the vapor space abovethe liquid is determined quantitatively against a blank using headspaceGC.

EXAMPLES Comparative Example 1 According to Patent Applications WO94/22500 and WO 94/22501

9.850 g of a commercially available absorbent (Favor®, companyStockhausen GmbH) is mixed thoroughly with 0.15 g of solidβ-cyclodextrin (beta-W7-cyclodextrin, technical grade, by Wackercompany). Thereafter, the extractable amount of cyclodextrin isdetermined according to the specified test method.

EA=93%

Comparative Example 2 According to Patent Applications WO 94/22500 andWO 94/22501

40 g of polyethylene glycol (m.w. 3000) is melted at elevatedtemperature. 40 g of cyclodextrin is added thereto, and the mixture ishomogenized. 9.40 g of a commercially available powdered absorbent(Favor®, company Stockhausen GmbH) is sprayed with 0.6 g of thecyclodextrin/polyethylene glycol solution, mixed thoroughly and cooledto room temperature. Thereafter, the extractable amount of cyclodextrinis determined according to the specified test method.

EA=89%

Example 1

-   A) An aqueous solution of acrylic acid (29.3 wt.-%) is mixed with    1.2 wt.-%/monomer of a polyglycol acrylate crosslinker mixture and    partially neutralized to 60 mole-% using a 50% sodium hydroxide    solution with stirring and cooling. The solution is cooled to    7-8° C. and purged with nitrogen for about 20 minutes. Following    addition of aqueous solutions of sodium persulfate, hydrogen    peroxide and a water-soluble azo initiator, the polymerization is    initiated with ascorbic acid, whereupon a significant rise in    temperature to more than 90° C. occurs. A gel-like product is    obtained.-   B) 50 g of the dried and milled polymer from A) screened to 150-800    μm is wetted with a solution of 0.5 g of ethylene carbonate, 2 g of    water and 4 g of acetone in a plastic vessel with vigorous stirring    and mixed thoroughly using a commercially available household hand    mixer (Krups company). Subsequently, the wetted polymer is heated in    an oven at a temperature of 180° C. for 30 minutes, thereby    undergoing surface crosslinking.-   C) The procedure is as described in A). In addition, however, 5 g of    cyclodextrin is added to the monomer solution. A gel-like product is    obtained, the further processing of which is effected as described    in B).-   D) The gel free of cyclodextrin, which has been obtained in A), is    immersed in a:80° C. hot solution in a beaker, consisting of 10 g of    cyclodextrin and 23.3 g of water, until the solution has completely    permeated into the polymer gel. Subsequently, the gel is willowed    and dried at 150° C.    EA=27%, determined according to the specified test method.-   E) 50 g of the dried and milled polymer from D) screened to 150-800    mm is wetted with a solution of 0.5 g of ethylene carbonate, 2 g of    water and 4 g of acetone in a plastic vessel with vigorous stirring    and mixed thoroughly using a commercially available household hand    mixer (Krups company). Subsequently, the wetted polymer is heated in    an oven at a temperature of 180° C. for 30 minutes.

The extractable percentage, EA=8%, determined according to the specifiedtest method, is clearly lower as a result of surface crosslinking.

Example 2

50 q of the willowed, dried and milled polymer from Example 1 A)screened to 150-800 μm is wetted with a solution of 0.5 g of ethylenecarbonate, 1.5 g of non-modified cyclodextrin, and 8.5 g of water in aplastic vessel with vigorous stirring and mixed thoroughly using acommercially available household hand mixer (Krups company). For surfacecrosslinking, the wetted polymer subsequently is heated in an oven at atemperature of 175° C. for 25 minutes.

EA=80%, determined according to the specified test method.

Example 3

-   F) In a 500 ml three-necked round bottom flask, 113.4 g of    β-cyclodextrin is suspended in 200 g of deionized water and 8 g of    an aqueous sodium hydroxide solution (50%). This suspension is    heated to boiling until all of the above is dissolved. With vigorous    stirring, 34.4 g of an aqueous solution of DIMAPA-quat. (60%) is    added dropwise over 30 min, and this is stirred under reflux for    another 5 hours. The solution is cooled to 5° C., and a pH of 7 is    adjusted using hydrochloric acid. The precipitate is filtrated and    washed with water. Following drying of the filter residue, the DS    value is determined to be 0.005 using elemental analysis. 50 g of    the willowed, dried and milled polymer from Example 1 B) screened to    150-800 mm is wetted with a solution of 0.5 g of ethylene carbonate,    1.5 g of cyclodextrin derivative according to F), and 7.3 g of water    in a plastic vessel with vigorous stirring and mixed thoroughly    using a commercially available. household hand mixer (Krups    company). For surface crosslinking, the wetted polymer subsequently    is heated in an oven at a temperature of 175° C. for 25 minutes.    EA=40%, determined according to the specified test method.    Determination of the Gas Concentration of Malodorous Compounds

Superabsorbers made of polyacrylic acid with a degree of neutralizationof 60% and 70%, respectively, and subjected to secondary surfacecrosslinking were modified in a second. secondary surface crosslinkingaccording to the procedure of Example 3, using various cyclodextrins.The amount of cyclodextrin can be inferred from the following Table. Inthe. measurement of malodorous substances, a polymer with nocyclodextrin was tested as a blank: according to the specified testprocedure, and the gas concentration of malodorous substance found wasset 100%. Samples containing cyclodextrin were subsequently tested andthe gas concentration of malodorous substance determined.

odorous Substance: Ethylfuran.

Reduction of ethylfuran concentration Wt.-% CD Cyclodextrin derivativein the gaseous space 10## β-Cyclodextrin 72%  3## β-Cyclodextrin 63% 3## α-Cyclodextrin 68% ##: Absorber having 60% neutralization of theacid groups

As can clearly be seen, the gas concentration of volatile substancesdissolved in water is reduced upon absorption by thecyclodextrin-containing polymers of the invention.

In analogy to ethylfuran, an odorous substance containing sulfur wastested.

In addition, the effect of pure cyclodextrin (with no polymer) wasmonitored. As can be seen, cyclodextrin in the polymer of the inventionfrom a content as low as 3% on achieves a marked reduction in the gasconcentration of the sulfur-containing compound.

Doping with Furfurylmercaptane:

Reduction of furfurylmercaptane Cyclodextrin or concentration in Wt.-%CD CD derivative the gaseous space  10# β-Cyclodextrin 42%  3#β-Cyclodextrin 51%  3# α-Cyclodextrin 65%  10## β-Cyclodextrin 46%   3##β-Cyclodextrin 18%   3## α-Cyclodextrin 28%  1.5#Monochlorotriazinyl-β-cyclodextrin 42%  3#Monochlorotriazinyl-β-cyclodextrin 49% 100  β-Cyclodextrin 57% 100 α-Cyclodextrin 64% #: Absorber having 70% neutralization of the acidgroups ##: Absorber having 60% neutralization of the acid groups

The polymers of the invention develop excellent effectiveness when thecyclodextrin is entrapped in the polymers:

Reduction of furfurylmercaptane concentration in Polymer of CD ratio thegaseous space Example [wt.-%] CD derivative [%] 1 E   1.5 non-modif. 721 E 3 non-modif. 55 3    3 of Ex. 3F 49

1. An absorbent polymer based on optionally partially neutralized,monoethylenically unsaturated monomers bearing acid groups, the surfaceof which polymer has been subjected to secondary crosslinking subsequentto polymerizing, wherein the polymer has cyclodextrins and/orcyclodextrin derivatives bound covalently and/or ionically theretoand/or incorporated therein.
 2. The polymer according to claim 1,wherein the polymer includes from 0.01 to 50 wt.-% of cyclodextrinsand/or cyclodextrin derivatives, relative to the polymer.
 3. The polymeraccording to claim 1, wherein a maximum of 85 wt.-% of the amount ofcyclodextrins and/or cyclodextrin derivatives in the polymer isextractable with water.
 4. The polymer according to claim 3, wherein theamount extractable with water is 60 wt.-% at maximum.
 5. The polymeraccording to claim 1, wherein the polymer is constituted up to 40 wt.-%of monoethylenically unsaturated monomers other than the monomersbearing acid groups.
 6. The polymer according to claim 1, wherein thepolymer has from 0.05 to 3 wt.-% of a crosslinking monomer incorporatedby polymerization.
 7. The polymer according to claim 1, wherein thepolymer has 30 wt.-% of a water-soluble, natural or synthetic polymerincorporated therein by polymerization and/or graft polymerization. 8.The polymer according to claim 1, wherein the polymer has been subjectedto surface crosslinking using from 0.1 to 10 wt.-%, relative to thepolymer, of a crosslinker component.
 9. The polymer according to claim1, wherein the polymer contains α-,β-, or γ-cyclodextrins or derivativesthereof as cyclodextrins or derivatives thereof.
 10. The polymeraccording to claim 1, wherein the cyclodextrins or cyclodextrinderivatives are covalently bound to the polymer via ethylenicallyunsaturated groups.
 11. The polymer according to claim 1, wherein thecyclodextrins or cyclodextrin derivatives are tonically bound to thepolymer via carboxylate, sulfate, sulfonate, or quaternary amino groups.12. The polymer according to claim 11, wherein the cyclodextrins orcyclodextrin derivatives are bound to the polymer in a cationic fashion.13. A process for producing the polymers according to claim 1 byfree-radical polymerization of an aqueous solution of the ethylenicallyunsaturated, optionally partially neutralized monomer bearing acidgroups, optionally up to 40 wt.-% of further monoethylenicallyunsaturated comonomers, crosslinking monomers, and optionally up to 30wt.-% of a water-soluble natural or synthetic polymer, optionalisolation, crushing, and drying of the polymer, wherein the cyclodextrinand/or cyclodextrin derivative is already contained in the polymerduring secondary surface crosslinking of same, or the polymer havingundergone surface crosslinking is treated with an ionic cyclodextrinderivative.
 14. The process according to claim 13, wherein thecyclodextrin and/or cyclodextrin derivative is incorporated prior to orduring polymerization of the monomers and/or applied on an optionallyobtained hydrogel and/or on optionally milled and dried polymer prior toor during surface crosslinking of the polymer.
 15. The process accordingto claim 13, wherein the cyclodextrin or cyclodextrin derivative isemployed as substance or as a solution.
 16. Use of the polymersaccording to claim 1 as an absorbent for aqueous liquids, preferably inabsorbing body fluids, in optionally foamed sheet materials, inpackaging materials, in plant breeding, and as soil improver.
 17. Theuse of polymers according to claim 16 in hygiene articles.
 18. Use ofthe polymers according to claim 1 as a vehicle and/or stabilizer foractive substances or fertilizers being released optionally in a delayedfashion.
 19. The polymer according to claim 2, wherein the polymercomprises from 0.1 to 30 wt. % of cyclodextrins, and/or cyclodextrinderivatives relative to the weight of the polymer.
 20. The polymeraccording to claim 2, wherein the polymer comprises from 0.5 to 10 wt.-%of cyclodextrins, and/or cyclodextrin derivatives relative to thepolymer.
 21. The polymer according to claim 4, wherein the amountextractable with water is 45% at maximum.
 22. A method of stabilizing anactive substance, comprising absorbing the active substance with thepolymer according to claim
 1. 23. An absorbent polymer compositioncomprising a polymer having polymerized units of one or moremonoethylenically unsaturated monomers having one or more acid groups,and one or more cyclodextrins, cyclodextrin derivatives, or both,wherein the polymer is secondary surface crosslinked and wherein thecyclodextrins and the cyclodextrin derivatives are at least covalentlybonded to the polymer, ionically bonded to the polymer or mixed with thepolymer.
 24. The composition of claim 23, wherein the polymerizedmonoethylenically unsaturated monomer units are neutralized.
 25. Thecomposition of claim 23, wherein the cyclodextrins or cyclodextrinderivatives are present in an amount of from 0.01 to 50 wt. %, relativeto the weight of the polymer.
 26. The composition of claim 23,comprising from 0.1 to 30 wt. % of one or more cyclodextrins,cyclodextrin derivatives, or both, relative to the weight of thepolymer.
 27. The composition of claim 23, comprising from 0.5 to 10 wt.% of one or more cyclodextrins, cyclodextrin derivatives, or both,relative to the weight of the polymer.
 28. The composition of claim 23,wherein at most of 85 wt. % of the cyclodextrins, cyclodextrinderivatives, or both, are extractable with water.
 29. The composition ofclaim 23, wherein at most 60 wt. % of the cyclodextrins, cyclodextrinderivatives, or both, are extractable with water.
 30. The composition ofclaim 23, wherein at most 45 wt. % of the cyclodextrins, cyclodextrinderivatives, or both, are extractable with water.
 31. The composition ofclaim 23, wherein the polymer comprises up to 40 wt. % of polymerizedunits of one or more monoethylenically unsaturated monomers other thanthe monoethylenically unsaturated monomers having acid groups.
 32. Thecomposition of claim 23, wherein the polymer further comprises from 0.05to 3 wt. % of one or more crosslinking monomers bonded to the polymer.33. The composition of claim 23, wherein the polymer comprises up to 30wt. % of a water-soluble, natural or synthetic polymer, polymerized orgraft polymerized to the polymer.
 34. The composition of claim 23,wherein the polymer is a crosslinked polymer obtained by contacting thepolymer with from 0.1 to 10 wt. % of a crosslinker component, whereinwt. % is relative to the weight of the polymer.
 35. The composition ofclaim 23, wherein the polymer comprises one or more α-, β-, orγ-cylodextrins or cyclodextrin derivatives.
 36. The composition of claim23, wherein the cyclodextrins or cyclodextrin derivatives are covalentlybonded to the polymer by ethylenically unsaturated groups.
 37. Thecomposition of claim 23, wherein the cyclodextrins or cyclodextrinderivatives are ionically bonded to the polymer by carboxylate, sulfate,sulfonate, or quaternary amino groups.
 38. The composition of claim 34,wherein the cyclodextrins or cyclodextrin derivatives are cationicallybonded to the polymer.
 39. A process for producing the composition ofclaim 23, comprising free-radical polymerization of an aqueous solutioncomprising one or more ethylenically unsaturated monomers having acidgroups, up to 40 wt. % of other monoethylenically unsaturatedcomonomers, and one or more crosslinking monomers to form a polymer,isolating and drying the polymer, then crosslinking the surface of thepolymer to form a surface crosslinked polymer, wherein one or morecyclodextrins, cyclodextrin derivatives, or both are (1) added to theaqueous solution prior to or during the free radical polymerization; (2)applied onto a hydrogel of the polymer; (3) applied to or on the driedpolymer; (4) applied to or on the surface crosslinked, dried polymer; or(5) applied to or on the surface of the dried polymer duringcrosslinking.
 40. The process according to claim 39, wherein thecyclodextrins or cyclodextrin derivatives are added or applied as asolid or as a solution.
 41. A method comprising absorbing aqueous fluidswith a composition according to claim
 23. 42. A process comprisingabsorbing an active substance onto the composition according to claim23, and then releasing the active substrate.
 43. A process ofstabilizing an active substance, comprising absorbing the activesubstance with the polymer composition according to claim
 23. 44. In ahygiene article, wherein the improvement comprises an absorbentcomprising the composition of claim 23.